Medical Technology

PSMA PET/CT Validated as Imaging Modality in Prostate Cancer

The use of a nomogram derived from prostate-specific membrane antigen (PSMA) PET/CT findings successfully predicted long-term outcomes for patients with high-risk or very high-risk prostate cancers according to a multicenter study published in JAMA Network Open.

The nomogram was utilized to determine the probability of any non-localized PSMA-based downstaging. It was based on four variables — initial prostate specific antigen level, biopsy grade group, percentage positive cores and clinical T categories to predict outcomes in 5275 patients who were referred to 15 tertiary centres in different countries. The outcomes included distant metastasis, prostate cancer-specific mortality, and overall survival.

The precision of the nomogram in determining the correct detect non-localized disease on PSMA PET/CT Imaging was as high as the area under curve (AUC), 0.75 (95%CI, 0.67 – 0.83).

Michael Xiang MD, PhD is the lead author and assistant clinical instructor in the Department of Radiation Oncology at University of California at Los Angeles. He pointed out that the nomogram provides indirect evidence of PSMA PET/CT imaging’s effectiveness.

“PSMA PET/CT imaging technology is revolutionary in the initial stage and staging, as well as management decisions of prostrate cancer,” stated Xiang in an interview to Medscape Medical News. “We don’t have any long-term information on how PSMA PET/CT findings could affect or influence downstream clinical outcomes like the emergence or death from prostate cancer or overall survival. These are the most important endpoints.”

Xiang utilized a UCLA-developed nomogram, or risk calculator, to assess the PSMA PET/CT’s prognostic information. “No patients in the current study had PSMA PET/CT imaging,” said Xiang. “Everything was predicted using the nomogram as a indicator of the predictive results if they were to get PSMA PET/CT (imaging). It was more of an indirect assessment.

The nomogram differs from other risk-stratification tools because it is used only in high-risk and very high-risk patients rather than in all-comers, according to Xiang. The nomogram was compared to the Cancer of the Prostate Risk Assessment groups, the Staging Collaboration for Cancer of the Prostate groups in stages, and the Memorial Sloan Kettering Cancer Center pre-prostatectomy nomogram that is based on five-year risk of progression of disease.

“This proxy for PSMA PET/CT (imaging) is extremely highly prognostic, and it outperforms existing risk stratification and prognostic tools for prostate cancer,” said Xiang, who noted one exception: the performance of the nomogram was comparable to STAR-CAP in predicting prostate cancer-specific mortality.

Xiang acknowledged a major weakness of the study. The researchers employed a proxy instead of actual results from PSMA PET/CT imaging. Another limitation is that the study was conducted retrospectively.

In the near future, additional factors such as molecular and genomic data could be used to help predict risks of outcome in extremely high-risk or high-risk patients, according Xiang.

Xiang said that “we would love to include more information , such as molecular tests and genomic data.” “The combination of our nomogram with genomic data will be more effective.”

Xiang said that the future directions could include using the nomogram in order to personalize the treatment of patients suffering from high-risk or high-risk prostate cancer.

“The goal is with more accurate prognostic information and risk stratification, we can offer more tailored therapies to patients according to their level of risk,” said Xiang. “We can turn these prediction tools into actionable items at the clinic.”

Thomas Hope, MD is associate professor in residence in the Department of Radiology and Biomedical Imaging School of Medicine, University of California at San Francisco. He noted that Xiang’s study demonstrates and confirms the importance of this particular nomogram.

“This work demonstrates the important prognostic value of PSMA PET/CT and supports the use of PSMA PET/CT in high-risk and extremely high-risk patients. It also shows the way that the nomogram can provide more value than other nomograms,” said Hope in an interview with Medscape Medical News. He was not involved in the study.

Hope pointed out that the nomogram could be of benefit to countries in which PSMA PET/CT isn’t readily accessible.

Hope and Xiang have not made any relevant disclosures.

JAMA Netw Open. 2021;4:e2138550. Full text

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